From DE 21 33 455 A1 and DE 23 62 190 A1, friction linings are known on the free surface of which an abrasive layer is provided which serves for evening out surface variations, particularly flute formations on the counterpart of the friction lining, by abrasion.
This flute formation is said to be evoked by insufficient possibilities for removing chips in case of surface contact of the frictional partners. Known abrasive layers consist of abrasive particles, e.g. carborundum, Al.sub.2 O.sub.3, pounce and the like, which are bound with one or several binders, modified phenolic resins or the derivatives thereof, such as cresol resin and the like.
The binding agents on the basis of natural or synthetic resins have thermo-setting properties and a temperature stability corresponding to that of the frictional material
From DE-A-23 62 190, it is known to give a wave-shaped configuration to the abrasive layer on the surface of the friction lining in order to provide for a reliable removal of chips in any operational state of the brake. The layer thickness of the abrasive layer amounts to approximately 0.3 to 0.6 mm.
So far, the known abrasive layers have been used in connection with brake pads containing asbestos.
Due to the legally regulated introduction of asbestosfree brake pads, new problems arise in practice during the operation of brakes equipped in such a manner.
Checks of such braking systems have shown that the wear behaviour at a low temperature is much more unfavourable than in case of brakes with asbestos-containing pads, i.e. the wear of the brake disk is higher at low working temperatures of the brake. This is particularly disadvantageous with vehicles in short-distance operation, wherein the brake arrangements do not reach elevated working temperatures, but also with vehicles driven over a long distance, wherein the brake arrangement may cool down completely between two braking processes.
FIG. 1 shows the quantitative wear behaviour V of the brake disk in dependence on the temperature [C.degree.] for asbestos-containing (a) and asbestos-free (b) brake pads in comparison. The different wear behaviour mainly depends on the working temperature of the brake arrangement.
The latter promotes the formation of nonuniform wear, namely differences in thickness, at the brake disk. These differences in thickness result in the so-called brake rubbing, i.e. in strong braking force variations during the braking process. This leads to vibrations of low frequency which may be transferred to the components of the entire vehicle and thus impair driving security and the service life of the brake arrangement.
According to present knowledge, these differences in thickness are produced by periodical contact of the pad with the rotating disk in the non-braked state. These may be caused, e.g., by tolerances of the brake arrangement with respect to measurements, withdrawal moments of the wheel brake cylinders or of axis components,
From DE 28 21 323 A1, a brake friction block is known wherein an intermediate layer being embedded in the friction lining is provided, which serves as heat barrier.